The heating of industrial buildings offers a considerable challenge to designers. If fuel is used to warm the air inside the building, then all air inside the building must be heated to provide a comfortable environment within the lower 2 meters--the area which is occupied by people.
By the very nature of warm air, it is less dense than the cooler air within the building and therefore the hot air leaving the heating source must rise. It is this occurrence which produces the wasteful stratification effect, where roof void temperatures can exceed the comfort level by as much as 20.degree. C.
Heat losses from the roof area are, therefore, very high since the temperature gradient is increased by up to 20.degree. C. In older buildings, where insulation values are much lower than today's modern structures with 0.7 W/m.sup.2 values, up to 90% of the heat generated within the building when passed to air as the transmitting medium can be lost from the upper, warmer parts of the building.
Radiant heating can provide at least equal and in most cases improved comfort conditions with large energy savings over systems using warm air.
Radiation is one of the basic mechanisms by which energy is transferred between regions of different temperature. It is distinguished from other methods of heat transfer, conduction and convection, by the fact that it does not depend upon the presence of an intermediate material to act as a carrier of energy. On the contrary, energy transferred by radiation is impeded by the presence of a material in the space between. Energy transferred by radiation is the consequence of energy carrying electro-magnetic waves.
Energy transmitted by radiation is converted into heat when it is absorbed. The energy carrying electromagnetic waves must, therefore, strike solid objects in order to be converted into heat energy.
The rate of radiant energy emission by a surface is dependent upon its absolute temperature. The rate of emission from one body to another is governed by their different absolute temperatures and this relationship is determined using the Stefan Boltzmann Law.
Over the years, three distinct forms of radiant heating system have developed which operate in three distinct temperature bands.
(1) Low temperature 60.degree.-175.degree. C. PA0 (2) Medium temperature 150.degree.-450.degree. C. PA0 (3) High temperature 800.degree.-950.degree. C.
The low temperature range comprises all systems using water or steam as the initial heat transfer medium.
The medium temperature range uses electric sheathed elements or radiant tubes (direct fuel fired and recirculated hot air ducts with all black surfaces).
The high temperature range uses incandescent electric or gas heated surfaces.